JPH09283006A - Cold cathode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold cathode having a low discharge voltage, and high efficiency and stability. SOLUTION: A cold cathode is prepared as follows: a raw material solution containing lanthanum nitrate La(NO3 )3 .6H2 O (S1) is prepared and applied on an electrode substrate (S2), the resulting film is subjected to preliminary reaction treatment in vacuum, at a temperature of ordinary temperature to 350 deg.C for about 30 minutes (S3), the electrode substrate is then heated in an electric furnace at a temperature of 700 deg.C to 750 deg.C so as to convert the raw solid film to an oxide crystalline film composed mainly of lanthanum oxide (S4). Then, the electrode substrate is treated in a reduction furnace to remove needless oxides therefrom (S5). The electrode substrate thus prepared is then cut and bent in a form of an electrode of the cold cathode fluorescent tube and assembled into the tube. In the cold cathode, the metal film as formed on the surface of the electrode, composed mainly of lanthanum oxide of lanthanum shows a high electron emission characteristic and sputter-resistance, so that it is useful as a cold cathode having a low discharge voltage, and a high efficiency and stability.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cold cathode.

[0002]

2. Description of the Related Art Conventionally, it is known that a fluorescent tube having a cold cathode that emits cold electrons and emits light as an electrode is used as a backlight of a liquid crystal display device. . In order to efficiently emit light from such a cold cathode fluorescent tube, various methods such as optimizing the gas composition and tube diameter sealed in the tube have been taken. Further, such a cold cathode fluorescent tube uses an electrode composed of a low work function element such as nickel (Ni) in order to emit light at a low discharge voltage, but the power consumption is still higher than that of the hot cathode fluorescent tube. There was a big problem. Since this nickel element has a sputtering property due to discharge, it adheres to the tube wall and shortens the light emission life. La _1-x Sr _x MnO
There have been reports of using lanthanoid-based perovskite type oxides having electrical conductivity such as ₃ as an electrode material, but they have not been sufficient in terms of discharge voltage and emission life.

Further, an oxide of R ₂ O ₃ type (R is a rare earth element, O is an oxygen element) used for a hot cathode is an insulator and is used in an electron emission mechanism such as an electrode for a cold cathode fluorescent tube. If an electron is emitted from the electrode by the tunnel effect using an electrode having such an insulator formed on the surface, it has been considered that sufficient discharge cannot be performed unless the insulator is set to a low film thickness of about several tens of angstroms.

An object of the present invention is to find out what means should be taken to obtain a cold cathode which is highly efficient and stable and has less spatter deposits on the tube wall.

[0005]

According to the first aspect of the present invention,
The cold cathode is characterized in that an oxide film containing a rare earth element and a conductive film are sequentially laminated on an electrode substrate.

The oxide film containing a rare earth element according to the present invention has a property that sputtering by discharge is unlikely to occur, so that the discharge life of the cold cathode can be extended. Also,
A discharge voltage can be reduced by providing a conductive film on this oxide film.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The details of a cold cathode and a method for manufacturing the same according to the present invention will be described below based on embodiments. (Embodiment 1) According to the present invention, an oxide film made of an oxide of a rare earth metal element and a metal film containing a rare earth metal element as a main component are formed on the surface of an electrode to reduce spatterability. It is intended to reduce the discharge voltage. FIG. 1 is a flowchart showing a method of manufacturing a cold cathode included in the cold cathode fluorescent tube of this embodiment. The present embodiment will be described below with reference to FIG. The present embodiment is an example in which lanthanum (La) is used as the rare earth metal element.

[0008] First, lanthanum _{nitrate: La (NO 3) 3 ·} 6
Dissolving of H ₂ O in a solvent such as water or an organic solvent to create a raw material solution (step S1). Here, the content ratio of La is adjusted so as to be 25 mol% or more when the raw material solution is prepared. As the organic solvent, for example, 1-methyl-2pyrrolidone or the like can be used.

Next, a raw material solution is applied to the surface of the electrode substrate, which is made of Ni-Cr (Inconel 601) and serves as an electrode substrate, by, for example, the spin coating method (step S).
2). At this time, the thickness of the coating film is 1000 to 2000 Å
Set to.

After that, the coating film is heated in a vacuum from room temperature to 35 ° C.
The temperature is raised to 0 ° C., and a preliminary reaction treatment is performed at 350 ° C. for about 30 minutes (step S3). Then, the coating process and the preliminary reaction process are repeated to form a raw material solid film having a film thickness of 3000 to 6000Å.

Next, the electrode substrate is placed in an electric furnace at 700-75.
A heat treatment is performed at a temperature of 0 ° C. to change the raw material solid film into crystals of an oxide film mainly containing lanthanum oxide (step S4).

Thereafter, the electrode substrate is subjected to a heat treatment at 600 to 650 ° C. for 10 minutes in a hydrogen atmosphere at a normal pressure in a reducing furnace to remove unnecessary oxides (step S5). At this stage, the surface of the crystallized oxide film is not metallized.

After that, the electrode substrate was cut into the shape of a cold cathode,
It is bent and processed. Then, the processed electrode is discharged in an inert gas with an atmospheric pressure of 50 to 90 Torr to form a metal film mainly containing lanthanum on the surface of the oxide film (step S6). At this time, the interface between the metal-based film and the oxide-based film is dense and continuous.

After such a discharge, electron spectroscopy was used to irradiate the surface of the electrode with X-rays to examine the energy state (measuring the chemical shift of the ESCA signal). It was confirmed that it was shifting to the side. That is, it was confirmed that the metal-based film was formed on the surface of the oxide-based film. Note that FIG. 2 shows step S
5 shows a state in which the oxide-based film 1 from which unnecessary oxides have been removed through 5 is formed on the electrode substrate 2. Also, FIG.
Shows a state in which the metal-based film 3 is formed on the surface of the oxide-based film 1 through step S6. In the figure, the broken line indicates the interface between the oxide-based film 1 and the metal-based film 3. At this time, since the surface of the oxide-based film 1 is changed to the metal-based film 3, the film thickness is reduced. As described above, the metal-based film 3 containing lanthanum as a main component is continuously laminated and formed on the oxide-based film 1 on the surface of the electrode, whereby the electrode drop voltage can be lowered.

Next, the cold cathode fluorescent tube of this embodiment was manufactured using the cold cathode manufactured by the above method. FIG.
1 shows an outline of the configuration of a cold cathode fluorescent tube of the present embodiment.
Reference numeral 11 in the figure denotes a cold cathode fluorescent tube, and the cold cathode 1 is placed in a glass tube 12 having an inner diameter of 12 mm and provided with a fluorescent material on the inner wall.
This is a configuration in which 3, 13 are arranged so as to face each other with an interval of 220 mm. In addition, 14 in the drawing is a cold cathode 1.
3 shows an electrode terminal of No. 3.

As a result of the discharge test of the cold cathode fluorescent lamp 11 as described above, discharge was generated at a voltage of about 300V. In comparison, the comparative cold cathode fluorescent tube in which the cold cathode was only nickel had a discharge voltage of about 350V. As described above, in the cold cathode fluorescent tube of the present embodiment, the discharge voltage could be reduced by about 50 V as compared with the comparative (conventional) cold cathode fluorescent tube. Therefore, according to this embodiment, a cold cathode fluorescent tube with low power consumption can be realized. Also,
Since an expensive rare earth metal element as a metal material can be easily used as a film on the electrode surface by thermally decomposing a relatively inexpensive rare earth nitrate, an increase in the manufacturing cost of the cold cathode fluorescent tube can be suppressed. Further, in the present embodiment, a step of discharging in an inert gas to form a metal-based film mainly containing lanthanum on the surface of the oxide-based film (step S
The metal-based film can be formed even if 6) is performed after this electrode is incorporated in the cold cathode fluorescent tube, and the manufacturing process can be further simplified.

Although the first embodiment has been described above, in the production of the cold cathode, the electrode substrate is subjected to a reduction treatment at 600 to 650 ° C. for 10 minutes in a hydrogen atmosphere at a normal pressure in a reduction furnace, which is unnecessary. Even if only the step of removing the oxide (step S5) is omitted, a cold cathode having similar characteristics can be produced. Further, in forming the cold cathode, the electrode substrate is subjected to heat treatment at a temperature of 700 to 750 ° C. in an electric furnace to change the raw material solid film into crystals of an oxide-based film mainly containing lanthanum oxide (step S4). Only the steps may be omitted. Further, in the production of the cold cathode fluorescent tube of Embodiment 1, only the step of subjecting the coating film to a preliminary reaction treatment at 350 ° C. for about 30 minutes in vacuum (step S3) may be omitted.

(Embodiment 2) In this embodiment, in addition to lanthanum nitrate: La (NO ₃ ) ₃ .6H ₂ O, manganese nitrate: Mn (NO ₃ ) ₂ .6H ₂ O is added and dissolved in a solvent. The manufacturing method is the same as that of the first embodiment except that a raw material solution is prepared. The graph of FIG. 5 shows the discharge voltage when the content ratio of La contained in the oxide film of the cold cathode manufactured by such a method is changed from 0 to 100%. The broken line in the figure shows the data of a conventional cold cathode fluorescent tube provided with an electrode made of only nickel (Ni). In addition, the same figure shows the relationship between the discharge voltage and the La content rate when the cold cathode fluorescent tube electrode prepared in the second embodiment is discharged for 1 hour and discharged for 289 hours. Shows.

From the graph of FIG. 5, it can be seen that when the La content in the oxide film is 25% or more, the discharge voltage is significantly reduced as compared with the La content of less than 25%. In addition, when the La content in the oxide film is 25% or more, the discharge voltage is about 300V, and the discharge voltage of the cold cathode fluorescent tube equipped with the nickel electrode is about 350V. It can be seen that the discharge voltage was significantly reduced.
By reducing the discharge voltage as described above, the power consumption of the cold cathode fluorescent tube can be reduced. In addition, in this embodiment, manganese nitrate: Mn (N
O _{3) 2} · 6H ₂ O and was prepared a raw material solution was added, for example, this may be added nitrates such as cobalt nitrate _{Co (NO 3) 2 · 6H} 2 O. At this time, the content rate of lanthanum needs to be set to 25 mol% or more. Thus, even if La and Mo or Co are mixed and the steps S1 to S6 shown in the first embodiment are performed, M
It is considered that o and Co are hardly combined with La and exist in the state of a mixture. Therefore, it is possible to select a mixed substance that is convenient for the cold cathode production process.

(Embodiment 3) FIG. 6 is a process sectional view showing a method of manufacturing a cold cathode used in a cold cathode fluorescent tube according to Embodiment 3 of the present invention. First, in the present embodiment, FIG.
As shown in (A), a thin metal layer 4 containing lanthanum (La) is formed on the surface of the electrode substrate 2 by, for example, a sputtering method. Then, as shown in FIG. 6B, the metal layer 4
A raw material solution containing lanthanum nitrate: La (NO ₃ ) ₃ .6H ₂ O was applied onto the above by the same method as in the above-described first embodiment, preliminarily reacted, and then crystallized in an electric furnace. After that, excess oxide is removed in a reducing furnace (step S1).
-Step S5). After that, by performing discharge in an inert gas (step S6), the metal-based film 3 is formed on the surface of the oxide-based film 1 as shown in FIG. 6 (C). Also in the present embodiment, the La content is adjusted to be 25 mol% or more when the raw material solution is prepared.

In this embodiment, since the metal layer 4 is interposed between the electrode substrate 2 and the oxide film 1, the discharge characteristics can be further improved. Also, the metal layer 4
Since the oxide-based film 1 and the oxide-based film 1 contain lanthanum, the interface after crystallization has a dense and continuous crystal structure, which has an advantage of improving electrical characteristics, particularly electron emission characteristics.

Next, an embodiment of a liquid crystal display device using such a cold cathode fluorescent tube as a backlight will be described with reference to FIG. Reference numeral 7 in the figure denotes a liquid crystal display device. In this liquid crystal display device 20, an upper glass substrate 23 and a lower glass substrate 24, which have liquid crystal driving electrodes arranged to face each other, are joined via a sealing material 25, and upper and lower glass substrates 23, 24 are provided.
A liquid crystal display panel 21 in which a liquid crystal 26 is sealed in a gap between the liquid crystal display panel 21 and a sealing material 25, and an illumination device (backlight) 22 arranged behind the liquid crystal display panel 21 (downward in the figure)
, And is roughly composed of As shown in the figure, the illuminating device 22 includes a light source 27 composed of a round tubular cold cathode fluorescent tube.
And the reflection film 2 that reflects the light emitted from the light source 27.
8, a light guide plate 29, and a light diffusion plate 30 that diffuses the light emitted from the light source 27 via the light guide plate 29. The light source 27 is arranged on one side edge side of the lighting device 22.

The round-tube cold-cathode fluorescent tube which is the light source 27 uses a cylindrical glass tube having an outer diameter of 2.6 mm, a distance between the cold-cathodes of 45 mm, and a disk-shaped cold cathode. . This cold cathode has a structure in which a lanthanum oxide crystal film is formed on the surface of an electrode substrate made of Inconel 601 (Ni-Cr-based material), and chromium and nickel are substantially continuous in the film thickness direction in the crystal film. Is formed. In the liquid crystal display device having such a configuration, the round-tube cold-cathode fluorescent tube, which is the light source 27, is stable in the state where the discharge voltage is low, so that the power consumption can be suppressed and the battery-integrated type long-time display is possible It is possible to realize a liquid crystal display device having excellent portability. Further, such a cold cathode is used in a field emission display (FED) or a direct current type plasma display (PDP).
Can also be applied.

Although the first to third embodiments have been described above, the present invention is not limited to these.
Various design changes accompanying the gist of the configuration are possible. For example, in each of the above-described embodiments, lanthanum is used as the rare earth metal element, but one or two kinds of rare earth metal elements may be used. The rare earth metal elements include yttrium (Y), scandium (Sc),
Cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (S
m), Europium (Eu), Gatrinium (Gd),
Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Lutetium (L
It is preferable to select a rare earth metal element having a low work function and a high vapor pressure temperature such as u). Table 1 below
The work function and vapor pressure (10-6 Torr) of these rare earth metal elements and nickel are shown.

[Table 1] Further, in the above-described third embodiment, the metal layer 4 is formed by the sputtering method, but a method of metallizing a thin oxide film by discharge may be used. Furthermore, the metal-based film 3 and the metal layer 4 described above may be in the form of a single metal element, an alloy of a plurality of types of metal elements, a mixture, or an intermetallic compound of these.

[0025]

As is apparent from the above description, according to the present invention, there is an effect of realizing a cold cathode having a low discharge voltage, high efficiency and high stability. Further, the surface of the electrode for the cold cathode fluorescent tube is formed of a substance having a good electron emission property and hardly sputtered, so that it is possible to prevent the sputtered substance from adhering to the tube wall of the cold cathode fluorescent tube.

[Brief description of drawings]

FIG. 1 is a flowchart showing a method for manufacturing a cold cathode according to Embodiment 1 of the present invention.

FIG. 2 is a cross-sectional view of essential parts showing the state of step S5 of the first embodiment.

FIG. 3 is a main-portion cross-sectional view showing a state of step S6 of the first embodiment.

FIG. 4 is an explanatory view showing an outline of cold cathode fluorescent lamps for a discharge test created in the first and second embodiments.

FIG. 5 shows the content ratio of La contained in the oxide film of the cold cathode in the cold cathode fluorescent tube prepared in Embodiment 2 from 0 to 100.
The graph which shows the discharge voltage when changing between%, and the discharge voltage of a prior art example.

FIG. 6 is a process sectional view of the third embodiment.

FIG. 7 is a sectional view of a liquid crystal display device having a light source including a cold cathode according to the present invention.

[Explanation of symbols]

 1 Oxide film 2 Electrode substrate 3 Metal film 4 Metal layer 11 Cold cathode fluorescent tube 12 Glass tube 13 Cold cathode

Claims (4)

[Claims] 1. A cold cathode comprising an electrode substrate, and an oxide film containing a rare earth element and a conductive film, which are sequentially laminated on the electrode substrate. 2. The cold cathode according to claim 1, wherein the conductive film is the rare earth element. 3. The cold cathode according to claim 1, wherein the oxide film is made of lanthanum oxide or yttrium oxide. 4. The cold cathode according to claim 1, wherein the conductive film is formed on the outermost surface.